The invention relates to a wireless network with a plurality of network nodes, each of which includes a radio device with a respective radio clock supply and is arranged to exchange data via a wireless medium, and also includes a user interface for the exchange of data between the associated radio device and at least one user.
A wireless network of this kind is known from the document xe2x80x9cTechnologie drahtloser Netzexe2x80x9d by Elmar Txc3x6rxc3x6k, Funkschau No. 22, 1998, pp. 20 to 25, which describes the configuration of a wireless network with a plurality of network nodes. A plurality of electrical apparatus, for example monitors, computers etc., is connected to a radio device in a network node via a user interface. Data is exchanged with other radio devices via the radio device of each network node. The cited document does not deal with clock synchronization of the applications executed in the network nodes.
It is the object of the invention to provide a wireless network in which the user clocks of the individual network nodes are synchronized to one another.
This object is achieved by means of a wireless network of the kind set forth in that
at least one user of a network node receives a user clock from a user clock supply of the relevant network node, which user clock is independent of the radio clock,
that each network node is arranged to determine, in response to events specified by a central network node, a time value related to the relevant user clock,
that the central network node is arranged at least to transmit the last time value formed by a selected network node, and
that each network node is arranged to form the difference between the last two time values determined and to realize frequency synchronization of its user clock supply in dependence on the comparison of the difference between its last two time values determined with the difference between the last two time values of the selected network node.
A wireless transmission is to be understood to mean herein a radio, infrared, ultrasound etc. transmission. In the wireless network synchronization of a user clock supply in a network node is realized via radio. The radio synchronization is independent of the synchronization of a user clock supply. In order to achieve this, a central network node initiates events which ensure that in a network node a time value is read from a user time counter which receives a user clock. In addition to the initiation of an event under the control of the central network node, a selected network node (referred to as the user master network node) distributes the last time value formed or the difference between the last two time values formed from the central network node. Subsequently, in a network node the difference is formed between the last two time values read out and the local difference result is compared with the difference result which is received from the central network node and originates from the user master network node. Because the difference results do not relate to the radio clock, the effect of the radio clock variations of the network node on the time and frequency synchronization of the user clock supply is eliminated.
Claim 1 relates to the formation of the difference in a network node while utilizing a user time counter. The selected network node should normally be a network node other than the central network node. In that case the user master network node (selected network node) supplies time data containing the difference result of the user master network node as disclosed in Claim 2.
The Claims 3 and 4 provide the correction value for a user clock supply which includes, for example a PLL (Phase Locked Loop) circuit. A mean value can then be formed so as to reduce disturbances in the transmission of the time data.
Claim 5 describes steps for synchronizing the user clock supply of a network node (hidden network node) by means of an intermediate network node when this network node cannot be reached by the central network node. The hidden network node determines a time value related to the user clock in response to the occurrence of a special event. The special event is transmitted by the intermediate node, for example via a radio synchronization signal. The Claims 6 and 7 disclose the correction value for a user clock supply of a hidden network node.
Claim 8 deals with steps to be taken when there are two sub-networks, each of which includes a central network node while and one sub-network includes the user master network node. The two sub-networks are interconnected via a bridge network node associated with both sub-networks. The network node of the second sub-network determines, upon occurrence of a predetermined event, a time value which is related to the user clock. The event is transmitted, for example, by way of a radio synchronization signal, by the central network node of the second sub-network. The Claims 9 and 11 disclose the correction value for a user clock supply of a network node of the second sub-network.
The Claims 11, 12 and 13 relate to the formation of the absolute time for the user clock in a network node of a single or first sub-network, in a hidden network node, and in a network node of a second sub-network.